Multi-level chiral edge states in Janus MXSSe (M = V, Ti; X = W, Mo) monolayers with high Curie temperature and sizable nontrivial topological gaps.

Quantum anomalous Hall (QAH) insulators with dissipation-less chiral edge channels provide ideal platforms for the exploration of topological materials and low-power spintronic devices. However, the ultralow operation temperature and small nontrivial gaps are the bottlenecks for QAH insulators towards future applications. Here, a new family of QAH insulators, that is, Janus MXSSe (M = V, Ti; X = W, Mo) monolayers, are proposed to be ferromagnets with large perpendicular magnetic anisotropy (PMA) and high Curie temperature above room temperature. Moreover, the present MXSSe monolayers hold sizable nontrivial topological gaps, resulting in the 1 chiral edge state with Chern number = -1. Unexpectedly, there also exists an occupied 2 chiral edge state below the Fermi level. Although all MXSSe monolayers retain their PMA characteristics on application of biaxial strain, various topological phase transitions are present. The VWSSe monolayer preserves the QAH state regardless of strain, while the VMoSSe and TiWSSe monolayers transform from QAH states to metallic states under tensile strains. The present MXSSe monolayers show competitive advantages among the reported materials for the development of topological electronic devices.